1. Field of the Invention
This invention relates to the detection of the presence of trichloroethylene (TCE) in soil or groundwater. More specifically, the invention is an in-situ system that can non-invasively detect if a plant has been exposed to TCE as an indication that TCE is present in the soil or groundwater.
2. Description of the Related Art
Trichloroethylene (TCE) is a chlorinated hydrocarbon which has been used in a variety of applications, most widely as an industrial solvent. However, TCE's toxicity to human and animal populations has been well documented. Accordingly, TCE has been banned in the food and pharmaceutical industries since the 1970s. Still, TCE is listed as one of the most prevalent groundwater contaminants in the United States, and is found at over 60% of the Environmental Protection Agency's National Priorities List (NPL) cites. Additionally, TCE's use in dry cleaning and as an industrial solvent indicates that there might be hundreds of small sites around the country where TCE has migrated into the soil and/or groundwater.
Currently, the main problems associated with detecting TCE in soil or groundwater is the time and cost involved. The traditional detection method involves going into the field and drilling monitoring wells, sampling the water over time, analyzing the data, collecting and analyzing samples again, analyzing groundwater flow patterns, and making a ‘best guess’ as to where the contaminant is located and how far it has moved. The costs associated with this process are significant as the cost associated with just the lab processing of each water sample is roughly $250.
Another approach to detecting TCE in groundwater is to check for the presence of TCE or trichloroacetic acid (TCAA) in plants. That is, it is well known in the phytoremediation field that plants take up TCE and metabolize it to form TCAA. More specifically, groundwater is taken up by plants and is a reactant in the photosynthesis process. If TCE is present in groundwater, evidence shows that the TCE is taken up by plants when absorbing groundwater. Plants then metabolize the TCE into multiple metabolites, with TCAA being the most prevalent in a plant's leaves.
While laboratory methods exist for the analysis of TCE in a plant's trunk, stems and leaves, these analysis methods are labor intensive, can be expensive, and/or can damage a plant. For example, tree cores have been used in some TCE detection methods. However, the act of taking a core from a tree risks introducing a fugal infection into the tree and also requires of use of special laboratory instrumentation. Since TCAA is more stable than TCE and can be sampled in a plant's leaves, some analysis methods have focused on a plant's leaves in order to avoid the drawbacks associated with using tree cores. However, the leaves have to be harvested, packed on ice, shipped to an analytical lab, and require a two day procedure to derivatize the TCAA so that it can be analyzed by gas chromotography. Further, even if a particular leaf has measurable levels of TCAA, this is not a dispositive indicator since each leaf from a plant can have different TCAA levels due to a variety of factors.